A storm earlier this may have shifted the pier and the tank, which had holes on its side.

The amount of oil discharged is still unknown. Wildlife has not been affected.

The sheen was spotted almost two weeks ago near the Cannery Pier Hotel. It has been concentrated in that area but was visible about 5 miles away at one point and has also been spotted on boats.

Madjeska told The Daily Astorian that oil from the tank was likely used for boilers at the Union Fishermen's Cooperative, which had been located at the pier and closed down more than 70 years ago.

Since then, the pier has had a handful of owners, and knowledge of the tank likely was lost somewhere in the turnover. The hotel now owns the property in the town that once hosted a booming cannery industry.

"We wish it had been disclosed, but it wasn't," hotel spokeswoman Donna Quinn said. "We don't know who knew or who didn't know."

Quinn said the hotel is researching options for how to pay for the cleanup and equipment. Madjeska estimates it will cost hundreds of thousands of dollars.

Madjeska said crews hope to fully access the tank by the end of the week and decide if it can be lifted.